Pathology of fathead minnows (Pimephales promelas) exposed to chlorine dioxide and chlorite

Fathead minnows (Pimephales promelas) were exposed to the biocide chlorine dioxide (0.13 and 0.19 mg l(-1)) for up to 12 h and to its primary decompos ition product, chlorite (177 and 304 mg l(-1)), for up to 96 h followed by recovery periods of up to 14 days. Chlorine dioxide exposure produced dose- dependent gill pathology including epithelial lifting, hypertrophy, hyperpl asia, lamellar fusion, and necrosis. Complete recovery, even in fish with s evere hypertrophy and lamellar fusion, was achieved within 4 days. Chlorite did not produce gill pathology even at a lethal exposure level (304 mg l(- 1) for 96 h) but did elicit a chronic inflammatory response with a marked i ncrease in circulating and fixed phagocytes within hematopoietic and vascul ar tissues. This study indicates that chlorine dioxide is approximately 100 0 times more toxic to fathead minnows than chlorite. Further, exposure of f athead minnows to these distinct but related compounds is consistently asso ciated with very different pathologies, (C) 2000 Elsevier Science Ltd. All rights reserved.